Not sure I understand how you use your leveling system. Winnebago recommends leveling side to side first, then front to back. Not sure your broken windshield has anything to do with this but just thought I would mention it.

My leveling system shows me which side, front or back is unlevel with a yellow indicator light. I always level which ever light is on first.

I find it hard to believe that using your leveling system is cracking your windshield unless there is some other underlining cause. Leveling the MH doesn't seem anymore severe than driving in and out of some driveways. Also, if you get a flat, your tire guy is going to jack up that corner of the MH. He will not jack up the entire side.

So, with that said, I read my Winnebago manual. Winnebago had 6 "Do Not" listed. Lifting the sides first versus the front/back was not one of them.

Pull back the rubber trim at the bottom of the glass and see if the crack started at the metal or rusted clip that the glass rests on. This will solve the mystery of what is going on. Follow crack to the end and check that also. Rkl